U.S. patent number 9,326,870 [Application Number 12/766,480] was granted by the patent office on 2016-05-03 for biodegradable stent having non-biodegradable end portions and mechanisms for increased stent hoop strength.
This patent grant is currently assigned to Medtronic Vascular, Inc.. The grantee listed for this patent is Joseph Berglund, Justin Peterson. Invention is credited to Joseph Berglund, Justin Peterson.
United States Patent |
9,326,870 |
Berglund , et al. |
May 3, 2016 |
Biodegradable stent having non-biodegradable end portions and
mechanisms for increased stent hoop strength
Abstract
A hybrid stent prosthesis including a biodegradable tubular
body, a first non-biodegradable self-expanding ring coupled to a
proximal end of the biodegradable body, and a second
non-biodegradable self-expanding ring coupled to a distal end of
the biodegradable body. The hybrid stent includes a mechanism for
longitudinally compressing the tubular body to increase the radial
or hoop strength thereof. The longitudinally compressing mechanism
may be protruding elements coupled to and extending radially
outward from the hybrid stent or elastomeric compression bands or
tethers extending between the non-biodegradable rings. The
compression bands may be pre-connected to both non-biodegradable
rings prior to stent delivery, or may be connected to one
non-biodegradable ring prior to insertion and connected to the
other non-biodegradable ring in situ.
Inventors: |
Berglund; Joseph (Santa Rosa,
CA), Peterson; Justin (Santa Rosa, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Berglund; Joseph
Peterson; Justin |
Santa Rosa
Santa Rosa |
CA
CA |
US
US |
|
|
Assignee: |
Medtronic Vascular, Inc. (Santa
Rosa, CA)
|
Family
ID: |
44022392 |
Appl.
No.: |
12/766,480 |
Filed: |
April 23, 2010 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20110264186 A1 |
Oct 27, 2011 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F
2/86 (20130101); A61F 2/07 (20130101); A61F
2/90 (20130101); A61F 2210/0004 (20130101); A61F
2002/8483 (20130101); A61F 2002/825 (20130101); A61F
2230/0054 (20130101); A61F 2250/0063 (20130101); A61F
2220/0016 (20130101); A61F 2/852 (20130101); A61F
2250/0031 (20130101) |
Current International
Class: |
A61F
2/06 (20130101); A61F 2/86 (20130101); A61F
2/848 (20130101); A61F 2/82 (20130101); A61F
2/07 (20130101); A61F 2/852 (20130101); A61F
2/90 (20130101) |
Field of
Search: |
;623/1.13-1.16,1.2,1.36,1.38 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2085050 |
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Aug 2009 |
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EP |
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WO00/41649 |
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Jul 2000 |
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WO |
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Primary Examiner: Rodjom; Katherine
Claims
What is claimed is:
1. A hybrid stent prosthesis comprising: a biodegradable tubular
body having a proximal end and a distal end; a first
non-biodegradable self-expanding ring coupled to the proximal end
of the biodegradable body; and a second non-biodegradable
self-expanding ring coupled to the distal end of the biodegradable
body; wherein the hybrid stent includes protruding elements having
a linear axis, the protruding elements only extend radially outward
at an acute angle from at least an outer surface of the first and
second rings away from a centerline of the stent transverse to the
longitudinal axis of the stent, wherein the protruding elements are
operable to lodge into tissue of a vessel wall to anchor the hybrid
stent therein, and wherein the lodged protruding elements permit
longitudinal contraction but prevent longitudinal expansion of the
hybrid stent after deployment to increase the radial strength
thereof.
2. The hybrid stent prosthesis of claim 1, wherein at least one of
the protruding elements is a loop.
3. The hybrid stent prosthesis of claim 1, wherein the protruding
elements radially extend from the hybrid stent at approximately
forty-five degrees.
4. The hybrid stent prosthesis of claim 1, wherein the protruding
elements are formed from a non-biodegradable material.
5. The hybrid stent prosthesis of claim 1, wherein protruding
elements are also coupled to and extend radially outward from the
biodegradable body.
6. The hybrid stent prosthesis of claim 1, wherein the
biodegradable body is formed from one or more filaments having a
pattern selected from braided, woven, wound, or knit.
7. The hybrid stent prosthesis of claim 1, wherein the
biodegradable body is self-expanding.
8. The hybrid stent prosthesis of claim 1, wherein the
biodegradable body is expandable via a user-applied compressive
force applied after the second ring is deployed at a treatment site
within a vessel.
9. The hybrid stent prosthesis of claim 1, wherein at least one of
the protruding elements is a ball.
10. The hybrid stent prosthesis of claim 1, wherein at least one of
the protruding elements is a rectangular arch.
11. The hybrid stent prosthesis of claim 1, wherein the protruding
elements are in a staggered pattern along the surface of the first
and second rings.
12. The hybrid stent prosthesis of claim 1, wherein the protruding
elements are in a random pattern along the surface of the first and
second rings.
13. A method of deploying a hybrid stent prosthesis at a treatment
site within a vessel, the method comprising the steps of: threading
a delivery catheter having the hybrid stent mounted at a distal end
thereof through a vascular system until the hybrid stent is located
adjacent to the treatment site, wherein the hybrid stent includes a
biodegradable tubular body, a first non-biodegradable
self-expanding ring coupled to a proximal end of the biodegradable
body, and a second non-biodegradable self-expanding ring coupled to
a distal end of the biodegradable body; and retracting a sheath of
the delivery system to deploy the hybrid stent at the treatment
site, wherein the hybrid stent is radially expanded and
longitudinally compressed upon deployment, wherein the hybrid stent
includes protruding elements having a linear axis, the protruding
elements only extend radially outward at an acute angle from an
outer surface of the hybrid stent away from a centerline of the
hybrid stent transverse to the longitudinal axis of the hybrid
stent, the protruding elements operable to lodge into tissue of a
vessel wall to anchor the hybrid stent therein and permit
longitudinal contraction but prevent longitudinal expansion of the
hybrid stent after deployment to maintain the hybrid stent in the
radially expanded and longitudinally compressed deployed
configuration to increase the radial strength thereof.
14. The method of claim 13, wherein the biodegradable body is
self-expanding and the step of retracting a sheath of the delivery
system to deploy the hybrid stent includes retracting the sheath
over the self-expanding biodegradable body.
15. The method of claim 13, wherein the step of retracting a sheath
of the delivery system to deploy the hybrid stent includes
retracting the sheath over the self-expanding second ring, and then
further retracting the sheath over the biodegradable body while
simultaneously applying a compressive force to the delivery system
to radially expand and longitudinally compress the biodegradable
body.
Description
FIELD OF THE INVENTION
The invention relates generally to endoluminal prostheses for
placement in a body lumen, and more particularly to a stent
prosthesis having a biodegradable body.
BACKGROUND OF THE INVENTION
A wide assortment of endoluminal prostheses have been developed,
each providing a uniquely beneficial structure to modify the
mechanics of a targeted lumen wall within a body lumen. As used
herein, "endoluminal prosthesis" is intended to cover a medical
device that is adapted for temporary or permanent implantation
within a body lumen, including both naturally occurring and
artificially made lumens. For example, stent prostheses are known
for implantation within body lumens to provide artificial radial
support to the wall tissue, which forms the various lumens within
the body, and often more specifically, for implantation within the
blood vessels of the body. A stent may provide long-term support
for damaged or traumatized wall tissues of the lumen or may be
implanted, for example, to maintain the patency restored to a blood
vessel that was clogged with atherosclerotic plaque. There are
numerous conventional applications for stents including
cardiovascular, urological, gastrointestinal, and gynecological
applications.
Essentially, stents are made to be permanently or temporarily
implanted. A permanent stent is designed to be maintained in a body
lumen for an indeterminate amount of time and is typically designed
to provide long-term support for damaged or traumatized wall
tissues of the lumen or to maintain the patency of a vessel clogged
with atherosclerotic plaque. A temporary stent is designed to be
maintained in a body lumen for a limited period of time in order to
maintain the patency of the body lumen, for example, after trauma
to a lumen caused by a surgical procedure or an injury or to
temporarily open a clogged lumen until natural healing occurs.
Permanent stents, over time, may cause irritation to the
surrounding tissue resulting in inflammation at the implant site
and restenosis, or re-narrowing of the vessel lumen. Further, if an
additional interventional procedure is ever warranted, a previously
permanently implanted stent may make it more difficult to perform
the subsequent procedure.
Temporary stents, on the other hand, avoid the complications
associated with long-term implants. Temporary stents may
advantageously be eliminated from body lumens after an appropriate
period of time, for example, after the traumatized tissues of the
lumen have healed and a stent is no longer needed to maintain the
patency of the lumen. Temporary stents may be made from
bioabsorbable and/or biodegradable materials that are selected to
absorb or degrade in vivo over time. Materials, typically
bioabsorbable polymers, and processes typically used to produce
bioabsorbable stents result in stents with low tensile strengths
and low modulus, compared to metallic stents of similar dimensions.
The limitations in mechanical strength of the bioabsorbable stents
can result in stent recoil after the stent has been inserted. This
can lead to a reduction in luminal area and hence blood flow. In
severe cases the vessel may completely re-occlude. In order to
prevent the recoil, polymeric stents have been designed with
thicker struts (which lead to higher profiles) or as composites to
improve mechanical properties. The use of relatively thick struts
makes polymeric stents stiffer and decreases their tendency to
recoil, but a significant portion of the lumen of the artery can be
occupied by the stent. This makes stent delivery more difficult and
can cause a reduction in the area of flow through the lumen. A
larger strut area also increases the level of injury to the vessel
wall and this may lead to higher rates of restenosis i.e.
re-occlusion of the vessel. Thus, current totally bioabsorbable
stents lack the mechanical properties to sustain vessel lumen size.
Even by design manipulation of past bioabsorbable braid
configurations and a selection of the best possible known
bioabsorbable materials, the totally bioabsorbable stent falls
short of current clinically proven products (i.e., metal
stents).
It is therefore an object hereof to provide a hybrid stent which
has mechanical properties desired in a stent, such as hoop or
radial strength, while maintaining at least a mostly bioabsorbable
structure. Such a stent provides sufficient support in a body lumen
for the duration of a therapeutically appropriate period of time,
after which the biodegradable portion then degrades to be
eliminated from the patient's body without surgical
intervention.
BRIEF SUMMARY OF THE INVENTION
Embodiments hereof relate to a hybrid stent prosthesis including a
biodegradable tubular body, a first non-biodegradable
self-expanding ring coupled to a proximal end of the biodegradable
body, and a second non-biodegradable self-expanding ring coupled to
a distal end of the biodegradable body. The hybrid stent includes a
mechanism for longitudinally compressing the tubular body and/or
maintaining the tubular body in a longitudinally compressed
configuration to increase the radial strength of the hybrid
stent.
BRIEF DESCRIPTION OF DRAWINGS
The foregoing and other features and advantages of the invention
will be apparent from the following description of embodiments
hereof as illustrated in the accompanying drawings. The
accompanying drawings, which are incorporated herein and form a
part of the specification, further serve to explain the principles
of the invention and to enable a person skilled in the pertinent
art to make and use the invention. The drawings are not to
scale.
FIG. 1 is a side view illustration of an embodiment of a hybrid
stent having a biodegradable body and non-biodegradable end
portions, wherein the hybrid stent is in a compressed or delivery
configuration.
FIG. 2 is an end view of the hybrid stent of FIG. 1.
FIG. 3 is a side view illustration of the hybrid stent of FIG. 1,
wherein the hybrid stent is in a radially expanded or deployed
configuration.
FIG. 4 is an end view of the hybrid stent of FIG. 1.
FIG. 5 is a side view illustration of an embodiment of a hybrid
stent including barbs on the non-biodegradable end portions for
increasing the hoop strength of the biodegradable body of the
stent.
FIG. 6 is an enlarged view of a barb attached to the hybrid stent
of FIG. 5.
FIG. 7 is a side view illustration of a hybrid stent including
barbs in a staggered or random pattern along the length of the
stent for increasing the hoop strength thereof.
FIGS. 8A-8C illustrate alternative configurations for the barbs of
FIG. 5.
FIGS. 9A-9C illustrate a method of deploying the hybrid stent of
FIG. 5 at a treatment site within a vessel, wherein the
biodegradable body of the stent is self-expanding.
FIGS. 10A-10D illustrate a method of deploying the hybrid stent of
FIG. 5 at a treatment site within a vessel, wherein the
biodegradable body of the stent is expanded by a compressive force
exerted by the operator.
FIG. 11 is a side view illustration of an embodiment of a hybrid
stent including pre-connected longitudinal compression bands for
increasing the hoop strength of the biodegradable body of the
stent.
FIGS. 12A-12C illustrate a method of deploying the hybrid stent of
FIG. 11 at a treatment site within a vessel.
FIGS. 13A-13B are side view illustrations of an embodiment of a
hybrid stent including longitudinal compression bands that are
connected to the stent in situ for increasing the hoop strength of
the biodegradable body of the stent.
FIG. 14 illustrates a portion of a longitudinal compression band of
FIG. 13A removed from the hybrid stent.
FIG. 15 illustrates a top-view portion of a proximal ring of the
hybrid stent of FIG. 13A, the ring including a slot for connecting
the longitudinal compression bands to the stent in situ according
to an embodiment hereof.
FIG. 16 illustrates a top-view portion of a proximal ring of the
hybrid stent of FIG. 13A, the ring including a slot and a flap for
connecting the longitudinal compression bands to the stent in situ
according to another embodiment hereof.
FIGS. 17A-17B illustrate a side-view portion of the proximal ring
of either FIG. 15 or FIG. 16.
FIGS. 18A-18C illustrate a method of deploying the hybrid stent of
FIG. 13A at a treatment site within a vessel and connecting the
longitudinal compression bands to the stent in situ, wherein a
distal end of the hybrid stent is essentially pulled in situ to
connect the bands to the stent, thereby longitudinally compressing
the stent and increasing the hoop strength thereof.
FIGS. 19A-19D illustrate a method of deploying the hybrid stent of
FIG. 13A at a treatment site within a vessel and connecting the
longitudinal compression bands to the stent in situ, wherein a
proximal end of the hybrid stent is essentially pushed in situ to
connect the bands to the stent, thereby longitudinally compressing
the stent and increasing the hoop strength thereof.
DETAILED DESCRIPTION OF THE INVENTION
Specific embodiments of the present invention are now described
with reference to the figures, wherein like reference numbers
indicate identical or functionally similar elements. The terms
"distal" and "proximal" are used in the following description with
respect to a position or direction relative to the treating
clinician. "Distal" or "distally" are a position distant from or in
a direction away from the clinician. "Proximal" and "proximally"
are a position near or in a direction toward the clinician. The
terms "biodegradable" and "bioabsorbable" are used in the following
description with respect to a property of a material.
"Biodegradable" is a material that is capable of being decomposed
or broken down in vivo and subsequently excreted. "Bioabsorbable"
is a material that is capable of being decomposed or broken down in
vivo and subsequently resorbed. Both biodegradable and
bioabsorbable materials are suitable for purposes of this
application and thus for simplicity, unless otherwise directed,
biodegradable materials and bioabsorbable materials will
collectively be referred to as "biodegradable" herein. In addition,
the term "dissolution" as used in the following description is
intended to refer to the breakdown of both biodegradable and
bioabsorbable materials.
The following detailed description is merely exemplary in nature
and is not intended to limit the invention or the application and
uses of the invention. Although the description of the invention is
in the context of treatment of blood vessels such as the coronary,
carotid and renal arteries, the invention may also be used in any
other body passageways where it is deemed useful. More
particularly, the stents are adapted for deployment at various
treatment sites within the patient, and include vascular stents
(e.g., coronary vascular stents and peripheral vascular stents such
as cerebral stents, superficial femoral artery stents and iliac
artery stents), urinary stents (e.g., urethral stents and ureteral
stents), biliary stents, tracheal stents, gastrointestinal stents
and esophageal stents. Furthermore, there is no intention to be
bound by any expressed or implied theory presented in the preceding
technical field, background, brief summary or the following
detailed description.
Referring now to FIGS. 1-4, a hybrid stent 100 includes a
non-biodegradable proximal end portion 102A, a biodegradable
midsection or body 104, and a non-biodegradable distal end portion
102B. Biodegradable body 104 degrades in situ as the vessel
remodels, leaving only non-biodegradable end portions 102A, 102B
within the remodeled vessel. The remodeled vessel then functions as
a normal vessel, i.e., with normal vasocontraction and other
processes, with an enlarged lumen. FIGS. 1-2 illustrate side and
end views, respectively, of hybrid stent 100 in a radially
compressed configuration for delivery to the treatment site and
FIGS. 3-4 illustrate side and end views, respectively of hybrid
stent 100 in a radially expanded or deployed configuration in which
hybrid stent 100 comes into contact with the vessel wall. When body
104 is deployed or radially expanded within a vessel, body 104
experiences foreshortening such that the length thereof decreases
as the diameter thereof increases. Such foreshortening is
illustrated by a comparison between the length of hybrid stent 100
in the radially compressed or delivery configuration of FIG. 1 and
the length of hybrid stent 100 in the deployed or radially expanded
configuration of FIG. 3.
End portions 102A, 102B include one or more non-biodegradable
radially compressible annular or cylindrical rings 106A, 106B,
respectively. Rings 106A, 106B are made from a non-biodegradable
self-expanding material, such as nickel-titanium alloy (nitinol) or
other superelastic metal alloys that bias end portions 102A, 102B
of hybrid stent 100 into apposition with an interior wall of a body
lumen when released from a restraining mechanism such as a
retractable sheath. Rings 106A, 106B may have any suitable
configuration including but not limited to a zig-zag or sinusoidal
pattern. In one embodiment, rings 106A, 106B may be similar in
design to the stent configuration of the Driver.RTM. bare metal
stent or the Endeavor.RTM. drug eluting stent, both of which share
the same basic configuration and are available from the assignee of
this application, Medtronic Vascular, Inc.
Body 104 of hybrid stent 100 extends between proximal end portion
102A and distal end portion 102B and is a generally hollow tubular
or cylindrical structure defining a lumen 112. As shown in FIGS. 2
and 4, the cross-sectional shape of body 104 may be circular.
However, the cross-sectional shape may alternatively be
ellipsoidal, rectangular, hexagonal rectangular, square, or other
polygon. An outer diameter of body 104 may be approximately equal
to or slightly larger than an inner diameter of a target body
vessel and may be substantially constant along the length thereof.
Body 104 is formed by one or more braided, woven, or wound
filaments 110. A typical hybrid stent 100 will comprise between 16
and 32 filaments, but more or less filaments may be used. In the
embodiment depicted in FIGS. 1 and 3, one set of filaments are in
the form of helices which are axially displaced in relation to each
other and have the center line of tubular body 104 as a common
axis. Another set of filaments are also in the form of helices,
which are axially displaced in relation to each other and also have
the center line of tubular body 104 as a common axis; however, the
second set of helices extend in the opposite direction relative to
the first set of helices. The two sets of filaments cross each
other at points in the manner shown in FIG. 1. It will be
appreciated by one of ordinary skill in the art that the
illustrated configuration of body 104 is exemplary and that various
configurations may be utilized in accordance herewith. For example,
filaments 110 may be employed in a wide variety of filament-based
stent configurations, particularly stents that contain coiled
and/or braided, knitted, or otherwise woven filaments. Some
suitable examples of stent structures are shown in U.S. Pat. No.
5,545,208 to Wolff et al. and U.S. Published Patent Application
Publication No. 2009/0306756 A1 to Cho et al., each of which is
incorporated by reference herein in its entirety.
Non-biodegradable end portions 102A, 102B may be attached to
biodegradable body 104 in any suitable manner, including bond(s),
weld(s), or the like. In one embodiment, a biodegradable suture or
polymer band may be tied around each ring 106A, 106B to anchor each
ring to the braided filaments 110 of body 104. In another
embodiment, a biodegradable adhesive may be utilized to couple end
portions 102A, 102B to body 104. Rings 106A, 106B may be coupled to
body 104 such that they partially or fully overlap the ends of body
104. Alternatively, rings 106A, 106B may be coupled to body 104
such that they extend proximally and distally, respectively, from
the ends of body 104 (not shown).
Body 104 of hybrid stent 100 is formed from a
bioabsorbable/biodegradable material that dissolves or breaks down
within a vessel. Suitable biodegradable materials include synthetic
and naturally derived polymers and co-polymers, as well as blends,
composites, and combinations thereof. Examples of suitable
materials include but are not limited to polylactide (PLA)
[poly-L-lactide (PLLA), poly-DL-lactide (PDLLA)], polyglycolide
(PLG or PLGA), polydioxanone, polycaprolactone, polygluconate,
polylactic acid-polyethylene oxide copolymers, modified cellulose,
collagen, poly(hydroxybutyrate), polyanhydride, polyphosphoester,
poly(amino acids), poly(alpha-hydroxy acid) or two or more
polymerizable monomers such as trimethylene carbonate,
.epsilon.-caprolactone, polyethylene glycol, 4-tert-butyl
caprolactone, N-acetyl caprolactone, poly(ethylene
glycol)bis(carboxymethyl) ether, polylactic acid, polyglycolic
acid, or polycaprolactone, fibrin, chitosan, or polysaccharides. In
one embodiment hereof, body 104 may be self-expanding due to the
inherent resiliency of particular biodegradable materials such as,
for example, poly-L-lactide, poly-D-lactide, polyglycolide, such
that filaments 110 return to an expanded state when released from a
compressed state. Each type of biodegradable polymer has a
characteristic degradation rate in the body. Some materials are
relatively fast-biodegrading materials (weeks to months) while
others are relatively slow-biodegrading materials (months to
years). The dissolution rate of filaments 110 may be tailored by
controlling the type of biodegradable polymer, the thickness and/or
density of the biodegradable polymer, and/or the nature of the
biodegradable polymer. In addition, increasing thickness and/or
density of a polymeric material will generally slow the dissolution
rate of the filaments. Characteristics such as the chemical
composition and molecular weight of the biodegradable polymer may
also be selected in order to control the dissolution rate of the
filaments. In one embodiment, filaments 110 are made from a
biodegradable polymer that is degradable within one year and that
has adequate mechanical properties to provide wall apposition and
strength for at least six months. Anti-fraying technology may
optionally be applied to the ends of filaments 110 to prevent
unraveling of braided body portion 104.
In an embodiment hereof, at least a portion of body 104 may be
coated with a therapeutic agent (not shown) such as a
controlled-release polymer and/or drug, as known in the art, for
reducing the probability of undesired side effects, e.g.,
restenosis. The therapeutic agent can be of the type that dissolves
plaque material forming the stenosis or can be such as an
antineoplastic agent, an antiproliferative agent, an antibiotic, an
antithrombogenic agent, an anticoagulant, an antiplatelet agent, an
anti-inflammatory agent, combinations of the above, and the like.
Such drugs can include zotarolimus, rapamyacin, VEGF, TPA, heparin,
urokinase, or sirolimus for example. Of course stent 100 can be
used for delivering any suitable medications to the walls of a body
vessel.
Non-biodegradable end portions 102A, 102B provide an outward radial
force against the vessel in which stent 100 is implanted. Due to
this radial force and the fact that end portions 102A, 102B
maintain their radial force even as body 104 is degrading over
time, end portions 102A, 102B resist longitudinal movement or
migration within the vessel. Therefore, the distance between end
portions 102A, 102B remains constant, thereby applying and/or
maintaining a longitudinal compressive force on body 104 such that
body 104 maintains sufficient radial or hoop strength as body 104
degrades over time. Enhanced hoop strength minimizes risk of stent
collapse, stent migration, enhances tissue-stent contact which
particularly beneficial when hybrid stent 100 includes a
therapeutic drug coating, and increases the vessel lumen diameter
after stent deployment.
Referring to FIGS. 5-6, a hybrid stent 500 includes a plurality of
protruding elements or barbs 508 extending radially outward from
end portions 102A, 102B of stent 500. Barbs 508 permit longitudinal
contraction/compression but prevent longitudinal expansion of
hybrid stent 500 after deployment, which results in increased
radial or hoop strength. More particularly, when hybrid stent 500
is deployed within a vessel, body 104 radially expands and
longitudinally contracts. Radial strength is directly related to
longitudinal contraction of body 104, and thus the radial strength
of stent 500 is increased when body 104 is longitudinally
contracted during deployment. However, due to the biodegradable
material of body 104, hybrid stent 500 may have a tendency to
longitudinally extend after hybrid stent 100 is deployed within a
vessel. If hybrid stent 500 longitudinally extends or lengthens,
body 104 radially contracts and the hoop strength of hybrid stent
500 decreases. Barbs 508 grip the tissue of the vessel wall and
anchor hybrid stent 500 therein to prevent ends 102A, 102B from
moving apart from each other, thereby maintaining the hoop strength
of longitudinally contracted body 104 after deployment.
As best shown in FIG. 6, each barb 508 is a loop that radially
flares at an acute angle from the outer surface of hybrid stent 500
so that when hybrid stent 500 is deployed, barbs 508 protrude into
the vessel wall and create an anchor that aids fixing hybrid stent
500 within the vessel. Barbs 508 located on rings 106A, 106B point
generally in a direction away from a centerline 510 of hybrid stent
500 after deployment, such that barbs 508 prevent movement of rings
106A, 106B away from each other (i.e., prevent longitudinal
extension of hybrid stent 500 after deployment), but permit
movement of rings 106A, 106B towards each other (i.e., permit
longitudinal contraction of hybrid stent 500 after deployment).
Specifically, each barb 508 radially extends from hybrid stent 500
at an angle O which is greater than zero degrees but less than
ninety degrees to prevent longitudinal extension but permit further
longitudinal contraction/compression of hybrid stent 500. As used
herein, angle O is measured from the outer surface of stent 500 in
a clockwise manner when barb 508 is located on first proximal ring
106A or anywhere between first proximal ring 106A and the
centerline 510 of stent 500 and angle O is measured from the outer
surface of stent 500 in a counter-clockwise manner when barb 508 is
located on second proximal ring 106B or anywhere between second
proximal ring 106B and the centerline 510 of stent 500. In one
embodiment, angle O is between thirty and sixty degrees. For
example, barbs 508 may radially extend from hybrid stent 500 at
approximately forty-five degrees. Barbs 508 may also serve as a
location or point of connection between biodegradable body 104 and
non-biodegradable end portions 102A, 102B.
Barbs 508 may be formed from a non-biodegradable material such as
nickel-titanium (nitinol) or other superelastic material that is
radially compressible for delivery of hybrid stent 100. In another
embodiment, it may be desirable to form barbs 508 from a
biodegradable material that is selected to absorb or degrade in
vivo over time. Biodegradable materials suitable for barbs 508
include magnesium or a magnesium alloy such as Magnesium AZ31 and
Magnesium WE43, other bioabsorbable metals, or bioabsorbable
polymers such as polylactic acid, polyglycolic acid, collagen,
polycaprolactone, hylauric acid, co-polymers of these materials, as
well as composites and combinations thereof.
Although illustrated as extending from end portions 102A, 102B, it
should be understood by those of ordinary skill in the art that
barbs 508 may be alternatively or additionally attached at any
location along the length of hybrid stent 500. For example, FIG. 7
illustrates a plurality of barbs 508 in a "random" or "staggered"
pattern along the cylindrical stent body for lodging hybrid stent
700 within the vessel when the stent is expanded.
Further, it should be understood by those of ordinary skill in the
art that barbs 508 may have any configuration suitable for gripping
and lodging within the tissue of the vessel wall. For example, FIG.
8A shows a protrusion element 808A having a flat or planar body
that flares or extends radially outwardly from ring 106B so that it
protrudes into the vessel wall and creates an anchor that aids
fixing the hybrid stent within the vessel. Further, FIG. 8B shows a
ball-type protrusion element 808B attached to ring 106B that is
operable to lodge into the vessel wall upon stent expansion and
create an anchor that aids fixing the hybrid stent within the
vessel. FIG. 8C shows a staple-like protrusion element 808C that
forms a rectangular arch or loop that flares or extends radially
outwardly from ring 106B to protrude into the vessel wall. The
configuration of barbs 508 is not limited to the configurations
illustrated herein.
Referring now to FIGS. 9A-9C, a method of deploying hybrid stent
500 having a self-expanding biodegradable body 104 within a vessel
920 is described. Stent deployment can be performed following
treatments such as angioplasty, or during initial balloon dilation
of the treatment site, which is referred to as primary stenting. As
shown in FIG. 9A, a sleeve or sheath 922 is provided to surround
and contain hybrid stent 500 in a radially compressed
configuration. Deployment of hybrid stent 500 is accomplished by
threading a delivery catheter 924 through the vascular system of
the patient until hybrid stent 500 is located adjacent to a
treatment site, for example, a lesion 926 which may include plaque
obstructing the flow of blood through vessel 920.
Once hybrid stent 500 is in position at the treatment site within
vessel 920, sheath 922 may be retracted or proximally withdrawn in
the direction towards the operator as indicated by directional
arrow 928 as shown in FIG. 9B. Since end portions 102A, 102B and
body 104 are all formed from a self-expanding material, each
portion of hybrid stent 500 radially expands by its own internal
restoring forces as sheath 922 is retracted to deploy hybrid stent
500 against the vascular wall of vessel 920 to maintain the opening
as is known to one of ordinary skill in the art. Further, barbs 508
will flare or radially extend from hybrid stent 500 as sheath 922
is retracted such that they protrude into the vessel wall. As
previously explained, body 104 radially expands and longitudinally
contracts as hybrid stent 500 is deployed within a vessel. FIG. 9C
illustrates hybrid stent 500 fully deployed within vessel 920. Once
implanted, barbs 508 grip the tissue of the vessel wall and,
together with rings 106A, 106B, anchor hybrid stent 500 within
vessel 920 to prevent undesired longitudinal extension, thereby
maintaining the hoop strength of longitudinally contracted body 104
after deployment.
FIGS. 10A-10D illustrate a method of deploying hybrid stent 500
when biodegradable body 104 does not self expand, but may also be
used with a body 104 of a stent that does self expand in order to
provide increased hoop strength. As shown in FIG. 10A, sheath 1022
surrounds and contains hybrid stent 500 in a compressed, reduced
size. Deployment of hybrid stent 500 is accomplished by threading
delivery catheter 1024 through the vascular system of the patient
until hybrid stent 500 is located adjacent to a treatment site, for
example, a lesion 926. Once hybrid stent 500 is in position at the
treatment site within vessel 920, sheath 1022 may be retracted or
proximally withdrawn in the direction towards the operator as
indicated by directional arrow 1028. Ring 106B of end portion 102B
will self-expand as shown in FIG. 10B as sheath 1022 is retracted
thereover. As ring 106B is deployed against the vascular wall of
vessel 920, barbs 508 will flare or radially extend from hybrid
stent 500 and protrude into the vessel wall.
With end portion 102B now anchored against the vascular wall of
vessel 920, sheath 1022 is further retracted or proximally
withdrawn in the direction towards the operator as indicated by
directional arrow 1028 while the operator simultaneously pushes or
distally advances a pusher or stopper 1032 in the direction away
from the operator as indicated by directional arrow 1030. Pusher
1032 may surround the inner member of delivery catheter 1024 or may
be formed as a shoulder (see FIGS. 9A-9B) on the inner member at
the proximal end of stent 500. Thus, with ring 106B anchored
against the vascular wall, ring 106A is moved closer longitudinally
to ring 106B, thereby applying a longitudinal compressive force
that radially expands and longitudinally contracts biodegradable
body 104 of hybrid stent 500 as shown in FIG. 10C. The longitudinal
contraction of body 104 results in increased radial or hoop
strength of hybrid stent 500. FIG. 10D illustrates hybrid stent 500
fully deployed within vessel 920. Once implanted, barbs 508 grip
the tissue of the vessel wall and anchor hybrid stent 500 within
vessel 920 to prevent undesired longitudinal extension, thereby
maintaining the increased hoop strength of longitudinally
contracted body 104 after deployment.
Referring now to FIG. 11, another mechanism for applying a
compressive force on braid 104 in the longitudinal direction in
such a way that the hoop or radial strength of the hybrid stent
increases is shown. A hybrid biodegradable and non-biodegradable
stent 1100 includes one or more pre-connected longitudinal
compression bands or tethers 1150 which actively compress the
biodegradable body 104 of hybrid stent 1100 to increase the radial
strength thereof. More particularly, a first end 1146 of
longitudinal compression band 1150 is connected to proximal ring
106A and a second end 1148 of longitudinal compression band 1150 is
connected to distal ring 106B. Longitudinal compression bands 1150
extend generally parallel to the longitudinal axis of hybrid stent
1100. Ends 1146, 1148 may be coupled to rings 106A, 106B,
respectively, by any suitable mechanical method. In one embodiment,
ends 1146, 1148 may be coupled to rings 106A, 106B, respectively,
with biodegradable sutures or polymers that are simultaneously
connecting end portions 102A, 102B to body 104 of stent 1100.
Longitudinal compression bands 1150 may be formed from a
biodegradable elastomeric material that essentially pulls or
squeezes rings 106A and 106B towards each other, thereby applying a
compressive force to biodegradable body 104 and increasing the hoop
strength of hybrid stent 1100. Suitable materials for longitudinal
compression bands 150 include but are not limited to cross-linked
PLG, cross-linked PLA, cross-linked PLGA, or other elastomeric
cross-linked bioabsorbable polymers with adequate mechanical
properties to longitudinally compress body 104 of hybrid stent
1100.
FIGS. 12A-12C illustrate a method of deploying hybrid stent 1100
having longitudinal compression bands 1150 within a vessel 1220.
Longitudinal compression bands 1150 are connected to rings 106A,
106B prior to hybrid stent 1100 being loaded into a delivery
catheter 1224. Delivery catheter 1224 includes a retractable sleeve
or sheath 1222 and may be similar to known delivery catheters for
delivery self-expanding stents. As shown in FIG. 12A, sheath 1222
is provided to surround and contain hybrid stent 1100 in a radially
compressed configuration. Radially compressing stent 1100 also
lengthens it. This radial compression stretches compression bands
1150 longitudinally. Compression bands 1150 thereby store energy
and, when released, exert a compression force on stent 1100 to
return to their unstretched configuration. Because compression
bands 1150 are stored in the stretched configuration within the
delivery catheter 1224, the material for compression bands 1150
should be selected to minimize the risk of stress relaxation in
longitudinal bands prior to use.
Deployment of hybrid stent 1100 is accomplished by threading a
delivery catheter 1224 through the vascular system of the patient
until hybrid stent 1100 is located adjacent to a treatment site,
for example, a lesion 1226. Once hybrid stent 1100 is in position
at the treatment site within vessel 1220, sheath 1222 may be
retracted or proximally withdrawn in the direction towards the
operator as indicated by directional arrow 1228 in FIG. 12B. End
rings 106A, 106B are formed from a self-expanding material such
that they radially expand by their own internal restoring forces as
sheath 1222 is retracted to deploy end rings 106A, 106B against the
vascular wall of vessel 1220. Body 104 may be formed of
self-expanding material such that it also self-expands when
released from sheath 1222. Alternatively, body 104 may not be
formed from a self-expanding material, and stored energy in
compression bands 1150 causes body to longitudinally compress as
stent 110 is released from sheath 1222.
FIG. 12C illustrates hybrid stent 1100 fully deployed within vessel
1220. Compression bands 1150 assist in radially expanding body 104
by longitudinal compression as stent 1100 exits sheath 1222,
thereby increasing hoop strength of body 104. Further, after stent
deployment longitudinal compression bands 1150 continue to exert a
compression force between 102A, 102B pulling them towards each
other to maintain and/or increase the hoop strength of
longitudinally contracted body 104.
FIGS. 13A-13B illustrate an embodiment of a hybrid stent 1300
having one or more longitudinal compression bands or tethers 1350
which are connected to hybrid stent 1300 in situ to actively
compress the biodegradable body 104 of hybrid stent 1300 to
increase the radial strength thereof. Similar to bands 1150,
longitudinal compression bands 1350 are formed from a biodegradable
elastomeric material that essentially pulls or squeezes rings 106A
and 106B towards each other to apply a compressive force to
biodegradable body 104 and increase the hoop strength of hybrid
stent 1300. Suitable materials for longitudinal compression bands
1350 include but are not limited to cross-linked PLG, cross-linked
PLA, cross-linked PLGA, or other elastomeric cross-linked
bioabsorbable polymers with adequate mechanical properties to
longitudinally compress body 104 of hybrid stent 1300. However,
unlike bands 1150, only a distal end 1348 of longitudinal
compression bands 1350 is connected to distal ring 106B of hybrid
stent prior to implantation, as shown in FIG. 13A. Longitudinal
compression bands 1350 include a stop or protrusion 1352 located
along the length thereof that becomes seated or lodged within
proximal ring 106A after hybrid stent 1300 is deployed at a
treatment site within a vessel, as shown in FIG. 13B. In one
embodiment, stop 1352 is a knot formed or tied onto band 1350. As
best shown in FIG. 14, the length L.sub.C of band 1350 between stop
1352 and distal end 1348 is selected/designed such that band 1350
will apply a longitudinal compressive force to hybrid stent 1300
and increase the radial strength thereof after stop 1352 becomes
seated within proximal ring 106A.
Hybrid stent 1300 may include multiple longitudinal compression
bands 1350. In one embodiment, the proximal ends of each band 1350
may be joined at a point 1354 and connected to a pull string 1356
that extends through the full length of the delivery system such
that when it is desirable to seat stops 1352 into proximal ring
106A, the operator may simply pull on a single pull string 1356 to
effectively pull all multiple longitudinal compression bands 1350.
In an alternative embodiment (not shown), the proximal end of each
longitudinal compression band 1350 may extend through the full
length of the delivery system such that the operator may
simultaneously or sequentially pull on each longitudinal
compression band 1350 to seat stops 1352 into proximal ring
106A.
Proximal ring 106A may include a key-hole or slot 1564 sized to
receive and contain stop 1352 of longitudinal compression band
1350. As shown in FIG. 15, ring 106A may include an extension 1562
that is attached or integral with ring 106A. Slot 1564 is formed
within extension 1562. Extension 1562 may extend generally parallel
to the central axis of ring 106A as shown in FIG. 17A or may be
inclined with respect to central axis of ring 106A as shown in FIG.
17B such that extension 1562 radially flares at an acute angle from
the outer surface of hybrid stent 1300. The incline or angle shown
in FIG. 17B may improve the seating of stop 1352 within slot 1564.
As will be explained in more detail herein, when it is desirable to
seat stop 1352 into proximal ring 106A the operator pulls on
longitudinal compression band 1350, optionally via pull string
1356, until stop 1352 "catches" and is lodged within slot 1564.
FIG. 16 illustrates an additional feature that may be utilized for
containing stop 1352 of longitudinal compression band 1350 within a
slot located on proximal ring 106A of hybrid stent 1300. Similar to
FIG. 15, proximal ring 106A includes a key-hole or slot 1664 formed
within an extension 1662 that is attached or integral to proximal
ring 106A. Extension 1662 may extend generally parallel to the
central axis of ring 106A as shown in FIG. 17A or may be inclined
with respect to central axis of ring 106A as shown in FIG. 17B such
that extension 1662 radially flares at an acute angle from the
outer surface of hybrid stent 1300. However, unlike FIG. 15, a
trap-door or flap 1666 is attached to proximal ring 106A and
extends within slot 1664. Flap 1666 is a flat or planar element
that has a shape or contour generally similar to the shape or
contour of slot 1664. When it is desirable to seat stop 1352 into
proximal ring 106A the operator pulls on longitudinal compression
band 1350, optionally via pull string 1356, until stop 1352 is
lodged or pinched between flap 1666 and extension 1662.
FIGS. 18A-18C illustrate a method of deploying hybrid stent 1300
having longitudinal compression band 1350 within a vessel 1820 and
connecting longitudinal compression bands 1850 to stent 1300 in
situ. The distal end of longitudinal compression bands 1350 are
connected to distal ring 106B of stent 1300 prior to hybrid stent
1300 being loaded into a delivery catheter 1824. Stops 1352 located
along the length of longitudinal compression bands 1350 are not yet
seated into proximal ring 106A of hybrid stent 1300. Delivery
catheter 1824 includes a retractable sleeve or sheath 1822 and may
be similar to known delivery catheters for delivering
self-expanding stents. As shown in FIG. 18A, sheath 1822 is
provided to surround and contain hybrid stent 1300 in a radially
compressed configuration. Deployment of hybrid stent 1300 is
accomplished by threading a delivery catheter 1824 through the
vascular system of the patient until hybrid stent 1300 is located
adjacent to a treatment site, for example, a lesion 1826.
Once hybrid stent 1300 is in position at the treatment site within
vessel 1820, sheath 1822 may be retracted or proximally withdrawn
in the direction towards the operator as indicated by directional
arrow 1828 in FIG. 18B. End rings 106A, 106B are formed from a
self-expanding material such that they radially expand by their own
internal restoring forces as sheath 1822 is retracted to deploy
rings 106A, 106B against the vascular wall of vessel 1820.
Biodegradable body 104 may also be made from self-expanding
material such that it radially expands as it is released from
sheath 1822. Alternatively, body 104 may not be formed from a
self-expanding material, and the operator may simultaneously apply
a compressive force by pulling pull string 1356 as sheath 1822 is
retracted or utilizing a pusher as described above. Thus,
longitudinal compression bands 1350 may be partially or fully
pulled proximally towards the operated as sheath 1822 is retracted.
Alternatively, once end portions 102A, 102B and body 104 are all
radially expanded or deployed within the vessel, longitudinal
compression bands 1350 are pulled in the direction towards the
operator as indicated by directional arrow 1828 via pull string
1356 until stops 1352 catch or lodge into proximal ring 106A of
hybrid stent 1300 as shown in FIG. 18B. Essentially, the distal end
portion 102B of hybrid stent 1300 is essentially pulled in situ to
connect bands 1350 to proximal ring 106A of stent 1300, thereby
longitudinally compressing the stent and increasing the hoop
strength thereof. Mechanisms for connecting bands 1350 to stent
1300 in situ include but are not limited to lodging stops 1352 into
a slot as described with respect to FIG. 15 or pinching stops 1352
between a slot and a flap as described with respect to FIG. 16.
With longitudinal compression bands 1350 coupled to hybrid stent
1300, longitudinal compression bands 1350 continue to exert a
compression force on ends 102A, 102B towards each other and
maintain and/or increase the hoop strength of longitudinally
contracted body 104.
Additionally, it is noted that the location of stop 1352 on
longitudinal compression band 1350 and the amount of pulling
performed by the user may determine the final radial diameter and
final length of deployed hybrid stent 1300. Specifically, if a
particular application requires a greater or lesser deployed
diameter for hybrid stent 1300, the length L.sub.C of longitudinal
compression band 1300 may be varied by adjusting the location of
stop 1352 on longitudinal compression band 1350 and the amount of
pulling performed by the user to achieve the desired deployed stent
dimensions.
FIG. 18C illustrates hybrid stent 1300 fully deployed within vessel
1820, with longitudinal compression bands 1350 now coupled to both
proximal and distal rings 106A, 106B of stent 1300. Longitudinal
compression bands 1850 are now cut or otherwise broken apart as
indicated by the gap shown at 1868 such that delivery catheter 1824
and pull string 1356 may be proximally retracted and withdrawn from
the patient. In one embodiment, delivery catheter 1824 may include
an integral cutting element for disengaging longitudinal
compression bands 1350 from pull string 1356. In another
embodiment, a separate cutting element may be delivered for
disengaging longitudinal compression bands 1350 from pull string
1356. As will be apparent to those of ordinary skill in the art,
other disengaging mechanisms may be utilized as well, such as for
example utilizing an energy source to break apart longitudinal
compression bands 1850 or forming weakened areas within
longitudinal compression bands 1850 that break apart upon
application of a sufficient pulling force by the user after stops
1352 are lodged within proximal ring 106A. After disengagement
occurs, hybrid stent 1300 having longitudinal compression bands
1350 attached thereto for increased hoop strength may remain in
situ.
FIGS. 19A-19D illustrate an alternative method of deploying hybrid
stent 1300 having longitudinal compression band 1350 within a
vessel 1820 and connecting longitudinal compression bands 1850 to
stent 1300 in situ. As explained above with respect to FIG. 18A,
the distal end of longitudinal compression bands 1350 are connected
to distal ring 106B of stent 1300 prior to hybrid stent 1300 being
loaded into a delivery catheter 1824. Stops 1352 located along the
length of longitudinal compression bands 1350 are not yet seated
into proximal ring 106A of hybrid stent 1300. As shown in FIG. 19A,
deployment of hybrid stent 1300 is accomplished by threading a
delivery catheter 1824 through the vascular system of the patient
until hybrid stent 1300 is located adjacent to a treatment site,
for example, a lesion 1826.
Once hybrid stent 1300 is in position at the treatment site within
vessel 1820, sheath 1822 may be retracted or proximally withdrawn
in the direction towards the operator as indicated by directional
arrow 1828. Ring 106B of end portion 102B will self-expand and
lodge against the vascular wall of vessel 1820 as shown in FIG. 19B
as sheath 1822 is retracted thereover. With end portion 102B now
anchored against the vascular wall of vessel 1820, sheath 1822 is
further retracted or proximally withdrawn in the direction towards
the operator as indicated by directional arrow 1828 while the
operator simultaneously pushes a pusher or stopper distally in the
direction away from the operator as indicated by directional arrow
1930 as shown in FIG. 19C. During this deployment step longitudinal
compression bands 1850 may be held or maintained under tension such
that proximal ring 106A of hybrid stent 1300 is essentially pushed
in situ to connect bands 1350 thereto, thereby longitudinally
compressing the stent and increasing the hoop strength thereof.
Mechanisms for connecting bands 1350 to stent 1300 in situ include
but are not limited to lodging stops 1352 into a slot as described
with respect to FIG. 15 or pinching stops 1352 between a slot and a
flap as described with respect to FIG. 16. With longitudinal
compression bands 1350 attached to hybrid stent 1300, longitudinal
compression bands 1350 continue to pull ends 102A, 102B toward each
other and maintain and/or increase the hoop strength of
longitudinally contracted body 104.
FIG. 19D illustrates hybrid stent 1300 fully deployed within vessel
1820, with longitudinal compression bands 1350 now coupled to both
proximal and distal rings 106A, 106B of stent 1300. Longitudinal
compression bands 1850 are now cut or otherwise broken apart as
indicated by the gap shown at 1868 such that delivery catheter 1824
and pull string 1356 may be proximally retracted and withdrawn from
the patient. As explained above with respect to FIG. 18C,
mechanisms for disengaging longitudinal compression bands 1350 from
pull string 1356 include an integral cutting element on delivery
catheter 1824, utilizing a separate cutting element, utilizing an
energy source to break apart longitudinal compression bands 1850,
or forming weakened areas within longitudinal compression bands
1850 that break apart upon application of a sufficient pulling
force by the user after stops 1352 are lodged within proximal ring
106A. After disengagement occurs, hybrid stent 1300 having
longitudinal compression bands 1350 attached thereto for increased
hoop strength may remain in situ.
While various embodiments according to the present invention have
been described above, it should be understood that they have been
presented by way of illustration and example only, and not
limitation. It will be apparent to persons skilled in the relevant
art that various changes in form and detail can be made therein
without departing from the spirit and scope of the invention. Thus,
the breadth and scope of the present invention should not be
limited by any of the above-described exemplary embodiments, but
should be defined only in accordance with the appended claims and
their equivalents. It will also be understood that each feature of
each embodiment discussed herein, and of each reference cited
herein, can be used in combination with the features of any other
embodiment. All patents and publications discussed herein are
incorporated by reference herein in their entirety.
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